Packaging machines, so-called tray closing machines are known in which products are packaged into pre-fabricated tray-shaped containers and closed with a film, for example from U.S. Pat. No. 7,290,380 B2. Furthermore, packaging machines that are able to form trays themselves from sheet material are known.
From a review article written by K. W. McMillin, ‘Where is MAP Going? A review and future potential of modified atmosphere packaging for meat’, published in Meat Science in the year of 2008, Vol. 80, pp. 43-65, several methods about modified atmosphere packaging (MAP), especially for meat products, have been known and discussed. Using the definition of the article, MAP is the removal and/or the replacement of the atmosphere surrounding the product before sealing in vapor-barrier materials. In general, a package protects products like meat against deteriorative effects including discoloration, off-flavor, off-odor development, nutrient loss, texture changes, pathogenicity, and other measurable factors. Usually, the consumer's decision whether to buy such a product depends on his optical impression of the product, preferably a bloomed red meat color as an important quality attribute.
On top of that, raw chilled meat during storage exhibits the chemical reactions of respiration, which is the active absorption of oxygen and release of carbon dioxide, but not as pronounced as for example for a muscle that is still alive. According to the article, it is generally supposed that the headspace must be approximately 1.5-2 times the meat volume and package collapse is to be prevented by headspace gas to meat volumes of 2 to 3. This is influenced by the absorption and the evolution of gas (e.g. oxygen, carbon dioxide, etc.).
In order to obtain the red meat color, commercially available packages typically contain a permeable film, usually leading to a very short shelf life. To prolong the shelf life, a so-called ‘motherbag’ is often used, which means a secondary packaging to have a low oxygen atmosphere during distribution. In the shops, the single packs are unpacked and the meat can start to bloom. Nevertheless, a difficulty with re-blooming of meat in such packages after low oxygen MAP storage has been inability to bloom and/or lack of color uniformity.
According to the pre-mentioned article, it is further known to use high-oxygen packages with a content of typically 60-80% oxygen, so that oxymyoglobin pigments can be maintained. Unfortunately, other oxidative reactions reducing the shelf life may be induced, too.